I am a remarried mother with three children. The oldest is almost 7 years old and I have a 2 1/2 year old and almost 3 month old with my current husband. My 6-year old son has been displaying behavioral problems for the past several months. I share custody with his father and we have a pretty good relationship with one another. He also is in a relationship, though not married, with a woman who has two daughters of her own. My son behaves when he is with his father, but displays poor behavior when he is with me, including defiance, a bad attitude and an overall depressed mood. He does things he knows not to do, he teases and starts fights with his younger sister and yells and talks back to me. I have tried all kinds of discipline, from time-outs to taking TV away to making him do chores around the house and not allowing him to play outside and nothing seems to phase him. His father and stepfather have had talks with him and behavior improves for a small time, but nothing long-term. I am at my wit's end, any suggestions?